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As I have been saying throughout this tutorial, Blender supports reuse and the ability to build up an Asset Library of all sorts of image assets. When you get into CG and Compositing and like that, another kind of asset emerges, and that's called node groups, and the ability to have standard sets of subroutines that process an image in a standard sort of way. So over here we have the Compositing view for one of the scenes from Big Buck Bunny, and if these little images here aren't showing, go ahead and click the Render button over there.
The Green is for Groups, just like in 3D view. The green here is for a node group. A node group is actually a set of nodes that have been grouped. We're going to go ahead and click right here. I'm going to zoom in here a little bit. To expand the group, click right there in the corner and the nodes that make up this group are now shown to you. So this is a standard node group that is used to process Franky, the antagonist in Big Buck Bunny.
What happens is the Ambient Occlusion pass comes in and it really doesn't matter what the noodle is. It's just a mini noodle. So we wanted every scene and every time we bring in his image, we want it to process it in a certain standard way, with a certain color correction applied to his material. So rather than go back to every scene and tweak his materials and like that, and then do all the re-rendering, now in post-pro we have a standard way to alter the colors of his appearance in our final video in post-pro.
So what we did is we created a node group here. You can ungroup the nodes by clicking here under Ungroup, or for the hot key, Alt+G to ungroup the nodes, and then the nodes when you do that should drop right back onto your Desktop. So now we can go ahead and add different nodes to the noodle or change the threads, whatever you want to do. Then when you're ready to make a group of nodes, you simply select the nodes. Do not include the Composite Output node in a node group, just as a word of warning.
Once you do that, then you can just make the group. You can rename the group by doing Ctrl+R or clicking Name and then typing in the name of the group that you want it to be. This is important, because this name is what's gets saved in the file, and then when you go into pull in; let's say we're working on shot number nine or scene number nine, we want to go in and pull in this node group when we do the File > Append or Link. Then when we navigate into that file.
That's the node group that's going to be shown. So the node groups are accessed by navigating to the file. When you go into the file, you will see an entry called Node Tree. When you click on that, then here is a list of all of the node groups that you can reuse to pull back into your composite. Now, the node groups, when you pull it in, the net effect of all of the input sockets is what's shown here on the outside line.
So this Add Note needs a socket, needs an Image Input. This Multiply needs a Factor Input, and this Invert needs an Image Input. So you thread this in, just like you would, in hardware you have what's called an integrated circuit, and you plug the circuit into the circuit board. Well, it's the same sort of thing that's going on now with software image processing is that you can build up these complicated circuits or mini noodles and reuse them over and over on different projects, and across the same project to provide consistent processing.
Once you're done, you can work directly in the node right here. I could go ahead and change the node and it recomputes the image. Then when it's done, I can just click anywhere outside the group and the node collapses back onto itself. That's how you use node groups within Blender to build up consistent processing and reusable processing of images in your final composite.
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